Heat generation is a significant concern with complex electronic components such as integrated circuits (IC's) (e.g., see U.S. Pat. No. 6,667,548). The amount of heat generated by a chip is related to the number of transistors on the device as well as the operation speed of the transistors. As transistor density and operating speed increases, so does heat generation. IC performance and reliability decrease as the temperature increases, so that it is important that the IC has adequate means for dissipating heat from the IC environment. Accordingly, thermal management of such IC's and related electronic components and devices are important so that the operating temperature is maintained at an acceptable level. However, as electronic devices continue to improve in capability and processing speed, requiring greater power demands, further improvements in thermal management are needed. Poor power dissipation is a significant constraint on the ability to develop circuits of continuously higher speed and/or power.
A number of thermal management techniques are known in the art, such as heat spreaders, heat sinks or heat pipes. U.S. Pat. No. 5,313,094 discloses dissipating thermal energy from isolated active silicon regions by filling a trench or hole with chemical vapor deposition (CVD) diamond material. Such heat spreaders and sinks are used to transfer generated heat from the device into the surrounding material, such as air or to a portion of the device where temperature does not affect operating characteristics. Heat sinks known in the art are typically made of a high thermal conductivity material (e.g., copper, aluminum, high thermal conductivity plastic) and may be designed to maximize the surface area exposed to ambient air to allow generated heat to be removed either by natural or forced convection (e.g., cooling fins, pins, etc., see U.S. Pat. No. 5,907,189).
Other thermal dissipation techniques involve etching a trench or hole through an active silicon region and an underlying dielectric layer to a supportive silicon substrate, oxidizing a trench wall, and filling the trench with a high thermal-conductivity material, such as diamond (e.g., see U.S. Pat. No. 7,170,164). Various back-side and front-side trench etching in semiconductor substrate for heat dissipation are known in the art (see, e.g., U.S. Pat. Nos. 7,029,951, 5,753,529, 5,757,081, 5,767,578, 7,170,164, 6,080,608).
Thermal conductivity of diamond is relatively high (e.g., 2200 W/m K, about twenty times greater than silicon and 5.5 times greater than copper) and so has been used in a number of applications as a heat sink or thermal regulating material (see, e.g., U.S. Pat. Nos. 5,648,148, 7,067,903, 7,170,164, 5,313,094, 5,907,189, 5,525,815). Diamond is also useful because it is readily formed through processes such as chemical vapor deposition (CVD) and by other attachment or deposition processes. Diamond need not be pure, but rather must have a higher thermal conductivity than the substrate to which the diamond is connected.
One disadvantage of conventional thermal dissipation techniques and devices is that those platforms are rather inflexible, with a result that fracture or other breakage occurs if the material is bent or strained. Accordingly, for applications where shape change is desired, such as in the field of flexible electronics or flexible integrated electronic devices on plastic substrates, thermal management can be difficult to achieve. In particular, the means for thermal regulation must be compatible with the flexible characteristics of the electronic system. Because thermal management techniques known in the art are inherently inflexible, they are generally not compatible with the field of flexible electronics. Conventional brittle thermal management systems cannot be integrated into an electronic device (e.g., flexible displays, electronic textiles, electronic skin) capable of deforming into many different shapes.
Another disadvantage is the difficulty in integrating diamond materials with products made using wafer-scale manufacturing. Thick diamond films on silicon substrates are always highly stressed unless great care is taken to minimize such stress by tailoring the deposition temperature and growth chemistry. Such processes inhibit further processing of the wafer due to excessive wafer bow (curvature of the wafer surface). Integration of other thin film materials with diamond further complicates the integration of diamond into products. Presented herein are various processes to circumvent these issues by integration of diamond as a thermal management material at the device level, which both maximizes the effectiveness of the diamond as a heat spreader and minimizes the amount of (relatively expensive) diamond needed to reduce the temperature of the active device to safe levels. Such integration can also occur at points closer to the end of the manufacturing sequence, thereby reducing the need for massive production redesign and thus facilitating earlier adoption of the technology.